This invention relates to a method and system for assessing the safety of rotors of a shrinkage fitted type, and, more particularly, to a method and system for assessing the safety of a rotor of a shrinkage fitted type, which is suitable for preventing the occurrence of accidents which might otherwise be caused by a reduction in shrinkage fitting force or power.
Heretofore, it has been usual practice to rely, for assessing the safety of rotors of a shrinkage fitted type, on a method which uses a stress intensity factor K based on the techniques of the elastic fracture mechanics. It is well known that the basic concept for this method is that fracture occurs when the stress intensity factor K reaches the material's constant K.sub.IC. However, materials have in recent years been developed with an eye to increasing their toughness, and this has made it impossible to neglect the phenomenon of plastic deformation occurring at a crack tip. Thus, there has been a tendency to doubt the usefulness of the method of assessing safety based on the elastic fracture mechanics which neglects the plastic deformation. As a result, a method of assessing safety based on the concept of J-integral in the elastic-plastic fructure mechanics has in recent years been used in place of the method of assessing safety based on the techniques of the elastic fracture mechanics. As described in "The Theory of Instability of the Tearing Mode of Elastic-Plastic Crack Growth" by P. C. Paris et al., this method is based on the concept that fracture occurs in a structure of high toughness when the J-integral around a crack tip reaches the materials's constant J.sub.IC (the elastic-plastic fracture toughness). The deformation behavior of a crack is such that the crack tip opens before fracture commences and considerable opening takes place in the entire crack. The higher the toughness of material, the more marked is the opening deformation behavior of a crack. Thus, with the tendency of increasing the toughness of materials in recent years, the opening deformation of a crack has raised a new problem. In a rotor of a shrinkage fitted type, for example, when a crack is formed at the disc fitting portion of a fitted member which is shrinkage fitted over a rotary shaft, shrinkage fitting force would be reduced by the opening of the crack before fracture of the fitted member occurs, with the result that there is play between the rotary shaft and fitted member. When this happens, the fitted member would vibrate and cause damage to stationary members (casing, stator blades, etc.) by contacting them. In methods of the prior art for assessing the safety of the rotors (K, J-integral), assessment has been made based on fracture occurring as a sequel to the development of a crack inherent in a structure and the problem noted hereinabove has not been taken into consideration. Thus, to achieve a safe operation of a rotor of a shrinkage fitted type formed with a crack, it is necessary to pay attention to a reduction in shrinkage fitting force which would be caused to occur by the opening deformation of the crack. There has hitherto been no proposal made to assess the safety of rotors of a shrinkage fitted type from this point of view.